1. Field of the Invention
The present invention relates generally to a method and apparatus for providing a combined steam boiler/combuster and gasifier. More particularly, though not exclusively, the present invention relates to a method and apparatus for a combined steam boiler/combuster and gasifier that cleanses emissions and provides co-generation of power from the burning of waste materials or low-grade coals.
2. Problems in the Art
Currently, there are many types of combined steam boiler/combuster and gasifier systems known in the art. However, the gasification process is the primary energy generation means. Gasification systems generally take materials, such as wood, coal, charcoal, agricultural residues, energy crops, municipal solid waste or other biomass materials, and gasify them to make a xe2x80x9cproducer gasxe2x80x9d used for power or electricity generation. A typical gasification system consists of a gasifier unit, filtering system, and an energy converter.
Steam boiler/combuster units are well-known, though their use as primary energy generation has been questionable for some time, mainly because of the harmful resultant emissions. A steam boiler/combuster creates high pressure steam used for power generation. Prior art systems apply steam boiler/combuster units as secondary energy generation means to gain energy and thus increased efficiency from the gases and char produced during the gasification process.
For example, U.S. Pat. No. 5,937,652 to Adelmalek, uses the gasifier as the primary energy converter. Adelmalek shows a gasifier that converts biomass fuel into a producer gas and char. The producer gas, generally a mixture of carbon monoxide, hydrogen and hydrocarbon, is then sent into a boiler and burned with the char to produce the high pressure steam needed to power a steam generator. Carbon dioxide is re-circulated into the gasifier. However, the flue gas from the boiler, containing other potentially harmful emissions, is allowed to escape into the atmosphere.
Similarly, in U.S. Pat. No. 5,626,638 to Valkanas, the gasification process is the primary means for energy conversion. Only the gases from the gasifier are used to power a gas turbine and to feed a steam generator. The flue gases from the steam generator are potentially harmful and yet are allowed to escape into the atmosphere. There is therefore a need for a method and apparatus that can provide useful power from biomass and other materials while minimizing the harmful emissions from the boiler.
Boilers used in prior art systems use carbonaceous fuels, typically, accepting the gases from the gasifier, for steam generation. However, there are currently certain fossil fuels and many types of waste material, such as shingles and used tires, that have fuel potential but are not used because of the high amounts of pollutants created during the combustion process. These are dirty fuels. For example, a typical used tire when burned directly creates an array of toxic byproducts such as dioxins, furans, PAHs, PCBs, hexavalent chromium, and cadmium. Other toxic byproducts from tire burning include mercury, lead, nickel, beryllium, xylene, toluene, phenol, mono-chlorobenzene, napthalene, formaldehyde and acetaldehyde. Similar observations can be made for bituminous coal. It is therefore preferable to gasify the tire and burn the gas which is much easier to control and clean.
In the case of solid waste, if these waste materials are not used, they typically wind up in city dumps or landfills. In 1998, there were over 270 million used tires. Putting these waste materials to use for energy production would significantly reduce the size of landfills. There is therefore a need for a method and apparatus for energy production that can use these products as fuel while minimizing the harmful emissions typically associated with burning these materials.
3. Features of the Invention
A general feature of the present invention is the provision of method and apparatus for providing a combined steam boiler/combuster and gasifier which overcomes the problems found in the prior art.
A further feature of the present invention is the provision of a method and apparatus for providing a combined steam boiler/combuster and gasifier which is capable of burning dirty fuels such as waste materials or low-grade coal.
A further feature of the present invention is the provision of a method and apparatus for providing a combined steam boiler/combuster and gasifier that uses two different types of fuel. Preferably, the primary fuel is a high-energy/high-polluting fuel used to generate most of the energy from the system, and the secondary fuel is a relatively low-energy/low-polluting fuel.
Another feature of the present invention is the provision of a method and apparatus for providing a steam boiler/combuster that can burn waste materials and low-grade coal combined with a gasifier to minimize harmful emissions.
A further feature of the present invention is the provision of a method and apparatus for providing a combined steam boiler/combuster and gasifier that can generate power from both the steam boiler/combuster and the gasifier.
A still further feature of the present invention is the provision of a method and apparatus for providing a combined steam boiler/combuster and gasifier wherein the steam boiler/combuster is the primary energy conversion means.
Another feature of the present invention is the provision of a method and apparatus for providing a combined steam boiler/combuster and gasifier wherein the biomass added to the gasifier is used to minimize the hazardous emissions from the steam boiler/combuster.
These, as well as other features and advantages of the present invention, will become apparent from the following specification and claims.
The present invention generally comprises a method and apparatus for providing a combined steam boiler/combuster and gasifier. In one embodiment, the steam boiler/combuster is fed waste materials such as shingles, tires, etc. The combustion process produces heat that generates steam for a steam turbine. The steam turbine turns a first generator that produces electricity.
The exhaust from the combustion process is fed into a gasifier. Biomass materials are added to the gasifier. The size and design of the gasifier and the amount of biomass materials added to the gasifier preferably is proportional to the amount of exhaust from the combustion process and the type of biomass fuel used in the gasifier. A majority of the heavy materials from the exhaust drop out during gasification. Burning both the exhaust from the combuster and the biomass materials produces ash and producer gas.
Pure oxygen may be added to the gasification process thereby turning the producer gas into synthesis gas that may be of higher energy. If high nitrogen products of combustion from the boiler furnace are recycled into the gasifier, the use of oxygen could keep further N2 addition down. An external source of heat may also be added to turn the producer or synthesis gas into a still higher energy pyrolysis gas. The producer, synthesis, or pyrolysis gas is then routed to an engine such as a micro turbine that turns a second generator. Thus, co-generation of electricity occurs from the burning of biomass and waste materials or low grade coal while harmful emissions are minimized.